1. Field of the Invention
The present invention relates to an internal combustion engine.
2. Description of the Related Art
An internal combustion engine obtains power by burning fuel in a combustion chamber. An “internal combustion engine” includes engines mounted in automobiles and gas turbine engines. In addition to internal combustion engines fueled by gasoline and other fossil fuels, internal combustion engines fueled by ammonia are known. In internal combustion engines fueled by gasoline etc., when burning the fuel, carbon dioxide is produced, but in internal combustion engines fueled by ammonia, even if burning the fuel, the production of carbon dioxide can be avoided.
Japanese Patent Publication (A) No. 5-332152 discloses an ammonia burning engine, able to burn ammonia gas to obtain a drive force, which is provided with an ammonia cracking reactor which uses the exhaust gas of the combustion chambers to crack the ammonia. The exhaust gas from the combustion chambers is used to heat a heat exchange pipe in the ammonia cracking reactor. It is disclosed that the ammonia gas which is led into the heat exchange pipe is cracked into hydrogen and nitrogen by an endothermic reaction which absorbs the heat of the exhaust gas. Further, the above publication discloses to lead the cracked hydrogen into a combustion chamber or a sub combustion chamber communicated with the combustion chamber. It discloses to use hydrogen gas with its excellent ignitability to make the ammonia gas effectively burn in the combustion chamber or sub combustion chamber and improve the combustibility of the difficult-to-burn ammonia gas.
In an internal combustion engine fueled by ammonia, by burning the fuel in the combustion chambers, nitrogen oxides (NOX) are produced. The exhaust which flows out from the combustion chambers contains not only unburned fuel, but also NOX. In an exhaust purification system of an internal combustion engine, by arranging a device able to reduce NOX in the engine exhaust passage, it is possible to remove the NOX which is contained in the exhaust.
For example, by arranging a three-way catalyst in the engine exhaust passage, it is possible to remove the NOX which is contained in the exhaust. When arranging a three-way catalyst in the engine exhaust passage, to improve the removal rate, it is preferable to perform control so that the air-fuel ratio at the time of combustion becomes the stoichiometric air-fuel ratio. However, precise control becomes necessary for maintaining the air-fuel ratio at the time of combustion at the stoichiometric air-fuel ratio.
On the other hand, to improve the heat efficiency of the internal combustion engine or reduce the amount of fuel consumption, it is preferable to operate the engine so that the air-fuel ratio at the time of combustion becomes lean. That is, it is preferable to perform lean combustion which burns the fuel in an air-rich state. However, when arranging a three-way catalyst in the engine exhaust passage of an internal combustion engine where the air-fuel ratio at the time of combustion becomes lean, the problem arises that the NOX removal rate becomes lower. Further, when using a three-way catalyst, platinum, palladium, and other expensive precious metals become necessary.